Aristotle
Aristotle is a simple business logic engine for Ruby. It's design goal is to stop clients from asking "How does this work?" and "Why does this happen?".
Aristotle achieves this by removing the line between business logic definitions and code. The same lines of text that are used to define logic rules can be displayed to the client without modification.
Aristotle is loosely inspired by cucumber. Check out the examples and screenshot below.
Aristotle grew out of the need we had at Apprentus to define and remember the ever increasing complexity with sorting and managing incoming requests from students.
Installation
Put this in your Gemfile
gem 'aristotle'
Usage
Create a folder app/logic and place inside files like:
app/logic/request.logic
Update the request state
Do nothing if the state was manually changed
Move to 'to_do' if the last message changed and is unverified
Move to 'failed' if the last message is sent and it is 'booking declined' or 'booking expired'
Move to 'deleted' if there are no messages in this requestapp/logic/request_logic.rb
class RequestLogic < Aristotle::Logic
# conditions
condition /the state was manually changed/ do |request|
request.state_changed?
end
condition /the last message changed and is unverified/ do |request|
request.last_message_id_changed? && request.state != :to_do && !request.last_message.try(:sent?)
end
condition /the last message is sent and it is 'booking declined' or 'booking expired'/ do |request|
last_message = request.messages.latest_first.first
last_message.present? && last_message.sent? && last_message.action.in?(:decline, :expire)
end
condition /there are no messages in this request/ do |request|
request.messages.count == 0
end
# actions
action /Do nothing/ do |request|
end
action /Move to '([a-z_]+)'/ do |request, folder|
request.state = folder.to_sym
end
endTo check that all the rules are defined, run aristotle from the command line. You'll get either:
$ aristotle
Checking RequestLogic
-> Everything is covered!
or
$ aristotle
Checking RequestLogic
class RequestLogic < Aristotle::Logic
# Update the request state:
condition /it's a non-HOT request with all the messages sent/ do |request|
end
end
To use the logic in your own models and controllers, do this:
class Request < ActiveRecord::Base
before_save :update_state
def update_state
RequestLogic.new(self).process 'Update the request state'
end
def update_state_and_get_what_i_just_did
command = RequestLogic.new(self).process('Update the request state', return_command: true)
command.action == 'the action that was performed'
command.condition == 'the condition that matched'
end
endDisplaying rules
To display a nice HTML version of the rules (e.g. in your admin interface for the client), run:
RequestLogic.html_rules(show_code: true)Here's an example. The box around is made by activeadmin.
Contributions
All contributions are very welcome!